A senior Thai policeman who headed an investigation into human trafficking for the country's military government has fled Thailand in fear of his life and is now requesting political asylum in Australia.

Major General Paween's inquiries have led to arrest warrants being issued for 153 people, including numerous local politicians, wealthy businessmen, four policemen, members of the Thai army, navy, police and the Internal Security Operation Command.

Ninety-one people have been charged and have begun appearing at trials in the capital, Bangkok.

One of the suspects was former senior army advisor Lieutenant General Manas Kongpan.

Major General Paween said the trials were now compromised.

"How can the witnesses believe that they will be protected for any period now?" he said.

And he believes the police have lost their nerve to prosecute the cases properly.

"I think the people there now will not be brave enough to continue," he said.

'Now I realise how dangerous it was'

Human Rights Watch Asia deputy director Phil Robertson said Major General Paween was the right man for the job.

"This is a person who investigates based on the facts on the ground and the evidence and follows the leads wherever they may go," he told 7.30

"So if they thought they were bringing someone in to give initial credibility to the investigation, then he would be deterred or pushed off from following the leads to their logical conclusion, I think they picked the wrong man."